In this proposal a new procedure for the direct selection of NADP-linked Glutamate dehydrogenase-less (am) mutants of Neurospora is described. This procedure makes the am gene one of only two in any Eucaryote in which it is possible to directly select both forward and reverse mutation and which has a sequenced protein product. Utilizing this procedure I will isolate new am mutants using the specific chemical mutagens: nitrous acid, ethylmethane sulfonate, ICR-170, N-methyl-N'-nitro-N-nitrosoguanidine and O-methylhydroxylamine. Spontaneous mutants will also be isolated. The new mutants will be characterized by means of: 1) reversion analysis with specific chemical mutagens; 2) assay of residual enzyme activity, if any, 3) assay for CRM production, 4) ability to form complementary heterocaryons and 5) suppression by super suppressors. A fine structure map will be constructed with these new alleles using both conventional analysis of flanking markers and deletion mapping. The new mutants and a detailed fine structure map which will result from this project will make it possible to pursue several lines of investigation into the basic nature of the Eucaryotic gene. The sequence homology of the gene product with glutamic dehydrogenases of vertebrates makes the analysis of this gene particularly relevant.